Pin rgb-lib contract import revision

[Jainakin]

Purpose

Make the contract-only RGB import API merged in UTEXO-Protocol/rgb-lib#68 available to RGB Lightning Node without introducing a second rgb-lib revision into the Lightning dependency graph.

Changes

• pin lightning to the immutable rgb-lib merge commit 79c0a97d20f9eac0b5d346f4e3c7d2715e424bc3
• pin lightning-invoice to the same exact revision
• no Lightning protocol, channel-funding, or runtime behavior changes

Keeping both crates on one immutable rgb-lib revision prevents duplicate RGB types and makes the downstream build reproducible.

Why this is still needed

Current rust-lightning dev uses rgb-lib tag v0.3.0-beta.32, which predates the contract-only import API. Until a later official rgb-lib release containing #68 is adopted, this pin is the bridge required by UTEXO-Protocol/rgb-lightning-node#128.

This PR is independent of the RGB funding-recovery stack in rust-lightning #32 and rgb-lightning-node #139/#140. It does not block or modify their recovery semantics.

Validation

Validated at de7dd6625:

• cargo check -p lightning -p lightning-invoice
• the resolved build uses rgb-lib commit 79c0a97d

Merge order

1. rgb-lib #68 is merged.
2. Merge this PR.
3. Advance the rust-lightning submodule in rgb-lightning-node #128 to the resulting rust-lightning dev commit.